The present invention relates generally to current sensing devices for electrical systems, and more particularly to timed reset fault indicators for alternating current power systems with multiple trip settings that are configured.
Various types of self-powered fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems and derive their operating power from inductive and/or capacitive coupling to the monitored conductor; and test point type fault indicators, which are mounted over test points on cables or associated connectors of the systems and derive their operating power from capacitive coupling to the monitored conductor.
Such fault indicators may be either of the manually resetting type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,956,873, 4,458,198, 4,495,489, 4,974,329, 5,677,678, 6,016,105, 6,133,723 and 6,133,724.
Detection of fault currents in a monitored conductor by a fault indicator is typically accomplished by magnetic switch means, such as a magnetic reed switch, in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the magnetic switch actuates a trip circuit that produces current flow in a trip winding to position an indicator flag visible from the exterior of the indicator to a trip or fault indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the target indicator to a reset or non-fault indicating position, or the fault indicator may be manually reset. Some prior art fault indicators also utilize light emitting diodes (LEDs) to display a fault condition.
Such prior art fault indicators have a single trip setting. This means that a plurality of different fault indicators need to be manufactured, inventoried and sold to meet customers' requirements for fault indicators with 25 ampere (A), 50 A, 10 A, 200 A, 400 A, 600 A, 800 A, 1000 A, 1200 A and 2500 A trip settings to monitor conductors that carry correspondingly different load currents.
There is therefore a need for a fault indicator with multiple trip settings that can determine the present load current level in a monitored conductor and select one of the trip settings that is appropriate for present load current conditions on the monitored conductor.
A need also exists for methods or techniques to configure the multiple trip settings of such a fault indicator.
Because of the compact construction and limited power available in self-powered fault indicators, it is preferable that the desired functions of the fault indicator be accomplished with minimal structure and with internal circuitry that has minimal current drain on a high capacity battery. The fault indicator must also provide highly reliable and extended operation over a number of years.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator that automatically selects one of a plurality of configured trip settings that is related to the load current in the monitored conductor.
Another object of the present invention is to provide a fault indicator that is capable of operating over a broad range of load currents, such as from about 5 A to about 1200 A.
Yet another object of the present invention is to provide a means of configuring each of the multiple trip settings of such a fault indicator.
Another object of the present invention is to provide a fault indicator that is microprocessor controlled, with the selection of the multiple configured trip settings under microcontroller control.
A further object of the present invention is to provide a fault indicator with a microcontroller that assists in the configuration of the multiple trip settings.